Trade-offs between leaf stoichiometric characteristics and photosynthetic traits of Larix gmelinii and its differences among provenances.

Variations and trade-offs between leaf stoichiometric characteristics and photosynthetic traits are indicative of ecological adaptation strategies of plants and their responses to environment changes. In a common garden of Maoershan, we measured leaf stoichiometric characteristics (carbon content (C), nitrogen content (N), phosphorus content (P), C/N, C/P, N/P) and photosynthetic traits (maximum net photosynthetic rate (Amax), maximum electron transport rate (Jmax), maximum carboxylation rate (Vmax)) of Larix gmelinii from 17 geographical provenances. We examined the provenance differences in stoichiometric characteristics and photosynthetic traits, and analyzed their trade-offs and influencing factors. The results showed leaf stoichiometric characteristics and photosynthetic traits significantly differed among provenances. The climatic factors of seed-source sites explained 54.8% and 67.2% of the variation in stoichiometric characteristics and photosynthetic traits, respectively. Aridity index (AI) of seed-source sites was positively correlated with C, N, P, Amax, Jmax, Vmax, but negatively with C/N, C/P, and N/P. Results of redundancy analysis showed that stoichiometric characteristics accounted for 75.0% of the variation in photosynthetic traits. Amax, Jmax, Vmax were positively correlated with C, N, P, and negatively correlated with C/N, C/P, N/P. The provenance differences in stoichiometric characteristics, photosynthetic traits, and their synergistic relationship suggested the long-term adaptation of trees to the climate of seed-source sites. These findings were of great significance for understanding ecological adaptation strategies of trees in response to climate change.

Provenance variation of root C, N, P, and K stoichiometric characteristics under different diameter classes of Larix gmelinii.

For exploring the difference of root stoichiometric characteristics among diameter classes and provenances, we examined the contents and stoichiometric ratios of carbon (C), nitrogen (N), phosphorus (P), and potassium (K) in three diameter classes of roots (0-1, 1-2 and 2-5 mm, respectively) of 39-year-old Larix gmelinii grown in a common garden. The results showed that root element contents and their stoichiometric ratios had significant difference among three diameter classes of roots. C content, C:N, C:P, C:K were the lowest, and N, P, K contents, N:P, and N:K were the highest in 0-1 mm diameter class roots. Compared with the 1-2 and 2-5 mm diameter class roots, 0-1 mm diameter class roots had different seasonal dynamics, which might be caused by the fact that 0-1 mm diameter class roots are absorptive roots and the other diameter class roots are transport roots. There was no provenance difference in C content among all diameter class roots, while significant provenance differences were found in N, K contents, C:N, and C:K in 0-1 mm diameter class roots, and great provenance differences for in P content, C:P, N:P, and N:K in 0-1 and 1-2 mm diameter class roots. N content, K content, C:P, N:P, and N:K in 0-1 mm diameter class roots had positive correlation with the aridity index of seed-source sites, while the P content, C:N and C:K had negative correlations. The stoichiometric characteristics were related with the diameter (or function) of roots, and had significant provenance differences in 0-1 mm (absorptive root) and 1-2 mm diameter class roots, which might be attributed to their genotypic adaptation to the environment of seed-source sites.

[Transcriptome analysis on responses of leaf photosynthesis and nitrogen metabolism of Larix gmelinii to environmental change]. / å ´å®‰è½å¶æ¾å¶å ‰åˆä¸Žæ°®ä»£è°¢å¯¹çŽ¯å¢ƒå˜åŒ–å“åº”çš„è½¬å½•ç»„åˆ†æž.

To reveal molecular mechanisms underlying photosynthesis responses of Dahurian larch (Larix gmelinii) to environmental changes, we used the high-throughput sequencing technology to sequence the transcriptome of larch leaves from four latitudinal sites with different environmental conditions, and compared differential expression genes (DEGs). The four sites from high- to low-latitude were Tahe (52°52' N), Songling (50°72' N), Heihe (49°22' N), and Dailing (47°08' N). A total of 282428811 clean reads were sequenced out, among which the abundace of DEGs were 16915, 18812, 28536, 20635, 29957 and 23617 for the Tahe-Songling, Tahe-Heihe, Tahe-Dailing, Songling-Heihe, Songling-Dailing, and Heihe-Dailing comparisons, respectively. The expression of nine Psb genes family (i.e., PsbB, PsbK, PsbO, PsbP, PsbQ, PsbS, PsbW, Psb27, and Psb28) encoding Photosystem Ⅱ and that of three genes (ATPF1A,atpA, ATPF1G, atpG, and ATPF1D, atpH) encoding F-type ATPase, which were involved in photosynthesis pathway, were significantly up-regulated with increasing environmental differences among the sites. A similar up-regulation pattern occurred for the expression of genes encoding glutamine synthetase (glnA, GLUL), nitrate reductase (NR), and carbonic anhydrase (cynT, can) that were involved in nitrogen metabolism pathway. The numbers of DEGs and up-regulated genes increased with the increases in environmental changes among the sites, resulting in inter-site divergence of photosynthetic capacity of larch trees.

[Temporal dynamics and influencing factors of soil microbes in Larix gmelinii forest soil during spring freezing-thawing period]. / æ˜¥å­£å†»èžæœŸå ´å®‰è½å¶æ¾æž—åœŸå£¤å¾®ç”Ÿç‰©çš„æ—¶é—´åŠ¨æ€åŠå ¶å½±å“å› å­.

Soil microbial community dynamics during the spring freezing-thawing period could affect carbon and nutrient cycling in the subsequent growing season. During spring soil freezing-thawing period, we monitored temporal dynamics of soil microbial community in different soil substrates for Larix gmelinii forest using phospholipid fatty acids (PLFAs) as biomarkers every 3-7 days. The results were as followed: 1) the total PLFAs content, the PLFAs content and relative abundance of each soil microbial group, the ratio of Gram-positive bacteria to Gram-negative bacteria (G+/G-), the ratio of saturated PLFAs to unsaturated PLFAs (S/NS) and the ratio of bacteria to total fungi (fungi + arbuscular mycorrhizal fungi) (B/F) all varied among sampling times; 2) soil total organic carbon (TOC) and nitrogen (TN) were the main factors affecting soil microbial community in the early stage of soil freezing-thawing period; soil moisture, TOC and TN were the main driving factors in the middle stage of soil freezing-thawing period; soil microbes were affected by soil tempera-ture, moisture, TOC, TN and C/N in the late stage of soil freezing-thawing period; 3) the total PLFAs content, the PLFAs content and relative abundance of each soil microbial group (except the relative abundance of bacteria), B/F, G+/G- and S/NS all showed significant difference between soil substrates, and soil TOC, TN and C/N were the key determination factors. Soil temperature, moisture, and nutrient availability were the main factors affecting soil microbial community during the spring soil freezing-thawing period, but the degree of influence varied with the freezing-thawing stages and microbial groups.

[Effects of latitudinal transplanting on temperature sensitivity of leaf dark respiration for Larix gmelinii.] / çº¬åº¦æ¢¯åº¦ç§»æ ½å¯¹å ´å®‰è½å¶æ¾é’ˆå¶æš—å‘¼å¸æ¸©åº¦æ•æ„Ÿæ€§çš„å½±å“.

Exploring the temperature sensitivity of leaf dark respiration is of significance for understanding forest carbon cycling and its response to climate change. However, its intra-specific variability and seasonality are not clear yet. In this study, we measured the temperature sensitivity coefficient (Q10) of leaf dark respiration for Dahurian larch (Larix gmelinii) that were transplanted from four latitudinal sites (i.e., Tahe, Songling, Heihe, and Dailing) in a common garden. Our specific aims were to explore the seasonal dynamics of Q10 and compare differences in Q10 among the indivi-duals from the four latitudinal sites. The results showed that the Q10 for the four sites exhibited similar seasonal trend, with the maximum Q10 in the middle growing season. The inter-site difference in Q10 was significant, ranging from (1.48±0.01) to (2.15±0.03). Furthermore, the inter-site difference showed the same pattern across the whole growing season, i.e., the warmer and lower latitudinal sites, the higher Q10. The Q10 was significantly and positively correlated with foliar nitrogen concentration and soluble sugar concentration, and mean annual temperature and mean annual precipitation in the transplanting sites. These findings suggested that the inter-site variation in Q10 and its seasonality could be mainly attributed to the foliar nutrient concentration and adaptation of trees to the climatic conditions of the transplanting sites, which should be considered in modeling and predicting responses of forest carbon cycling to climate change.

[Carbon and nitrogen storages and allocation in tree layers of Fraxinus mandshurica and Larix gmelinii plantations].

By the methods of wood analysis and sequential soil core, the biomass and productivity of the tree layers in 20-year old Fraxiuns mandshurica and Larix gmelinii plantations, as well as the carbon (C) and nitrogen (N) storages in the above- and below-ground organs of the stands, were estimated. The biomass of F. mandshurica and L. gmelinii was 6815.10 g x m(-2) and 9295.95 g x m(-2), in which, stem occupied 57.32% and 58.01%, and fine roots occupied 2.67% and 1.80%, respectively. The annual productivity of F. mandshurica and L. gmelinii was 1618.16 and 2102.45 g x m(-2) x a(-1), in which, stem accounted for 39.34% and 46.70%, and fine roots accounted for 12.06% and 5.25%, respectively. The C content in the organs of F. mandshurica was lower than that of L. gmelinii, while the N content was in adverse. The C storage of F. mandshurica was lower than that of L. gmelinii, while the N storage had no significant difference between the two tree species. The biomass, productivity, and C and N storages of aboveground organs were lower for F. mandshurica than for L. gmelinii, indicating the higher construction efficiency of the aboveground part of L. gmelinii. Due to the significant differences in the C and N contents between tree species and between the organs of same tree species, the measurement should be made on different tree species and different organs to have an accurate estimation of forest C and N storages.

[Effects of nitrogen fertilization on fine root lifespan of Fraxinus mandshurica and Larix gmelinii].

Root observation tubes (minirhizotrons) were used to study the effects of nitrogen addition on the fine root growth of Fraxinus mandshurica and Larix gmelinii, with the correlations between the fine root lifespan and nitrogen availability analyzed. After the nitrogen addition, the fine root number of F. mandshurica and L. gmelinii had a decreasing trend, but the fine root diameter became larger and the branching ratio decreased. The survival rate of F. mandshurica fine roots increased, and the median root lifespan prolonged 105 days, compared with the control. No significant responses to the nitrogen addition were observed in the survival rate of L. gmelinii fine roots. The first-order fine roots with smaller diameter, the roots in surface soil (0-15 cm), and the fine roots newly born in spring and summer were vulnerable to extend their lifespan by nitrogen addition, suggesting that the fine roots with higher physiological activity were easily to be affected by nitrogen fertilization.

[Effects of nitrogen fertilization on ectomycorrhizal infection of first order roots and root morphology of Larix gmelinii plantation].

In this paper, the first order roots of Larix gmelinii plantation under N fertilization were sampled from different soil depths in different seasons to study their morphology under effects of ectomycorrhizal fungi. The results showed that the infection rate of ectomycorrhizal fungi on the first order roots was significantly affected by soil N availability, soil depth, and season. N fertilization induced a decrease of the infection rate, and the decrement varied with soil depth and season. In comparing with the control, the infected first order roots had an obvious variation of their morphology, e. g., averagely, root diameter increased by 18.7%, root length decreased by 23.7%, and specific root length decreased by 16.3%, which differed significantly with N application rate, soil depth, and season. The infection of ectomycorrhizal fungi changed the first order root morphology of L. gmelinii, which might substantially affect the physiological and ecological processes of host plant fine roots.